Dario Fo wrote the satirical farce Morte accidentale di un arnicho in 1970 following a scandal in his native Italy. In December 1969, a bomb exploded in Milan killing 16 people. Police arrested several suspected left-wing agitators, one of whom mysteriously fell to his death while in custody. Despite a public outcry and damning evidence of foul play, subsequent investigations concluded that Guiseppi Pinelli's demise was either "accidental" or suicide.

In Fo's play, the 'absent hero' is never named and does not appear. Set at the police station in question after his death, it falls to a delusional maniac to champion the cause of truth and expose the force's own crime - at best, ineptitude and harassment, at worst, murder.

Because of its grounding in the events of its time, there's a danger of fossilisation with Accidental Death of an Anarchist. Director Robert Delamere tackled that dilemma head on, commissioning this new translation by Simon Nye (best known for penning seminal TV sitcom Men Behaving Badly) which, to put it mildly, has taken some liberties.

Entering the auditorium, the usually open Donmar stage is shrouded by a three-sided curtain, but even before the curtain rises, it's clear Delamere and Nye have wrested Fo's tale of corruption from its 1969 Italian setting and plunked it into modern Britain. We hear snatches of Tony Blair and the Queen, then a warped recording of "Jerusalem", the needle screeching off at the "green and pleasant land" bar as the opening scene is revealed with a Spiderman-suited maniac (played by Rhys Ifans) clambering through a window into a shabby police room (designed by Simon Higlett).

Delamere coaxes strong performances from his ensemble. Paul Ritter, Adrian Scarborough and Cornelius Booth achieve a Marx Brothers-esque cohesion as the easily duped trio of cops - their anarchist singalong is priceless - while a battered Desmond Barrit seems to be the only one who recognises the madman for what he is.

What a madman, too. Fully trained at the ministry of funny walks, accents and other affectations, Ifans displays immense energy in rolling a litany of loopy characters - including a professor (named Creutzfeldt Jakob), a police sergeant, a bishop, a prosthetic-wielding war veteran and, most importantly, an investigating judge-cum-country squire - into one lunatic with a love for "the theatre of life".

Yet for all the cast's accomplished zaniness, at two and three-quarters hours, this evening is something of an endurance test. The eliciting of fabrications and retractions, which forms the bulk of Act One and reopens Act Two, goes on too long, becoming overly preachy and repetitive. More problematic is the central premise. While alleged police corruption and bungling is hardly uncommon, how often do arrests - let alone, accidental deaths - of anarchists occur in modern Britain?

Given the abundant additions of modern references, you would have thought Nye and Delamere could have gone further still by trimming judiciously and swapping the anarchist for perhaps an Iraqi terrorist, a peace protestor or even a Labour backbencher, say. Talk about topicality.

- Terri Paddock